Here are simplified steps for flashing a GSI:
1. Flash disabled_vbmeta.tar
Use Odin to flash disabled_vbmeta.tar in the AP slot. If prompted to wipe the device, do so and reboot.
2. Flash TWRP or Fastbootd Recovery
Flash TWRP or Fastbootd recovery with Odin in the AP slot. After flashing, press Volume+ and Power, and release Power at the Samsung logo to enter recovery mode.
3. Enter Fastboot Mode
In recovery, select "enter fastboot" or, in TWRP, choose "reboot" then "fastboot."
4. Connect Device to PC
Connect your device to a PC with ADB and Fastboot tools installed.
5. Prepare GSI
Download and extract the GSI .img file. Rename it to gsi.img.
6. Flash GSI
Run these commands:
fastboot erase system
fastboot delete-logical-partition product
fastboot flash system gsi.img
fastboot reboot recovery
7. Disable Encryption or Factory Reset
In TWRP, flash FBE and format data.
For Fastbootd, factory reset the device and reboot.
8. Boot into GSI
The device should now boot into the GSI system if compatible.